U.S. patent number 7,826,593 [Application Number 12/519,565] was granted by the patent office on 2010-11-02 for collimator.
This patent grant is currently assigned to C-Rad Innovation AB. Invention is credited to Anders Brahme, Roger Svensson.
United States Patent |
7,826,593 |
Svensson , et al. |
November 2, 2010 |
Collimator
Abstract
A collimator (1) primarily adapted for usage in a narrow scanned
pencil beam radiation therapy system (100) includes adjacent pairs
(5) of collimator leaves (10, 20). An inner portion (12) of a
collimator leaf (10) facing the opposite leaf (20) of a pair (5) is
made of a first material having high linear radiation attenuation.
The remaining, major portion (14) of the leaf (10) is made of a
second material having a comparatively low density, weight and
radiation attenuation. The collimator (1) provides effective
penumbra trimming of a radiation beam (60), while simultaneously
protecting healthy tissue around a tumor in an irradiated patient
(80) from the radiation. The new design results in a significantly
more compact, lighter and less expensive collimator (1) as compared
to traditional collimators.
Inventors: |
Svensson; Roger (Varmdo,
SE), Brahme; Anders (Danderyd, SE) |
Assignee: |
C-Rad Innovation AB (Uppsala,
SE)
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Family
ID: |
39536549 |
Appl.
No.: |
12/519,565 |
Filed: |
December 7, 2007 |
PCT
Filed: |
December 07, 2007 |
PCT No.: |
PCT/SE2007/001090 |
371(c)(1),(2),(4) Date: |
August 10, 2009 |
PCT
Pub. No.: |
WO2008/076035 |
PCT
Pub. Date: |
June 26, 2008 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20100034357 A1 |
Feb 11, 2010 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60875535 |
Dec 19, 2006 |
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Current U.S.
Class: |
378/65;
378/152 |
Current CPC
Class: |
G21K
1/046 (20130101); A61N 5/1042 (20130101); G21K
1/04 (20130101); A61N 5/1037 (20130101); G02B
27/30 (20130101) |
Current International
Class: |
A61N
5/10 (20060101) |
Field of
Search: |
;378/65,145,146,147-153 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2403884 |
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Jan 2005 |
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GB |
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03079373 |
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Sep 2003 |
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WO |
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Other References
International Search Report dated Apr. 17, 2008. cited by
other.
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Primary Examiner: Song; Hoon
Attorney, Agent or Firm: Young & Thompson
Claims
The invention claimed is:
1. A radiation gantry comprising: a radiation generator for
generating an input radiation beam; a radiation target; a beam
scanning system for directing and scanning said input radiation
beam onto said radiation target to form a narrow scanned pencil
radiation beam having full width of half maximum of no more than 32
mm; a collimator for sharpening a penumbra of said narrow scanned
pencil radiation beam, said collimator comprising at least one pair
of collimator leaves, wherein: a penumbra-trimming portion of a
collimator leaf facing an opposite collimator leaf of a collimator
leaf pair is made of a first metal or a first alloy of said first
metal having a first linear radiation attenuation coefficient and
said first metal has a first atomic number according to the
periodic table of the elements, said penumbra-trimming portion
having a thickness in a range of about 10 to 50 mm in the direction
of said narrow scanned pencil radiation beam; and a remaining
support portion of said collimator leaf is made of a second metal
or a second alloy of said second metal having a second linear
radiation attenuation coefficient that is lower than said first
linear radiation attenuation coefficient and said second metal has
a second atomic number that is lower than said first atomic
number.
2. The radiation gantry according to claim 1, wherein said
radiation generator is arranged for providing an electron beam
having an energy content of at least 50 MV.
3. The radiation gantry according to claim 1, wherein said
radiation target has a thickness of about 2 to about 5 mm in the
direction of said input radiation beam.
4. The radiation gantry according to claim 1, wherein said
radiation target is made of a low atomic number material having an
atomic number no larger than 40.
5. The radiation gantry according to claim 1, wherein said
penumbra-trimming portion has a thickness in a range of about 15 to
30 mm in said direction of said narrow scanned pencil radiation
beam.
6. The radiation gantry according to claim 5, wherein said
penumbra-trimming portion has a thickness in a range of about 15 to
25 mm in said direction of said narrow scanned pencil radiation
beam.
7. The radiation gantry according to claim 1, wherein said narrow
scanned pencil radiation beam has full width of half maximum of not
more than 16 mm.
8. The radiation gantry according to claim 1, wherein said
collimator comprises multiple adjacent pairs of collimator leaves
and wherein: a first side of said collimator leaf facing a first
neighboring collimator leaf comprises a longitudinal shoulder
adapted for running in a longitudinal groove of said first
neighboring collimator leaf; and a second opposite side of said
collimator leaf facing a second neighboring collimator leaf
comprises a longitudinal groove adapted for engaging a longitudinal
shoulder of said second neighboring collimator leaf.
9. The radiation gantry according to claim 1, wherein said first
metal or said first alloy of said first metal is selected from
tungsten, osmium and iridium or an alloy of at least one of
tungsten, osmium and iridium.
10. The radiation gantry according to claim 1, wherein said second
metal or said second alloy of said second metal is selected from
steel and aluminum.
11. The radiation gantry according to claim 1, wherein an upper
portion of said penumbra-trimming portion extends a first distance
into said collimator leaf and a lower portion of said
penumbra-trimming portion extends a second distance into said
collimator leaf, said second distance being shorter than said first
distance.
12. The radiation gantry according to claim 1, wherein an end side
of said penumbra-trimming portion facing said opposite collimator
leaf comprises a groove designed for engagement with a shoulder
protruding from a penumbra trimming portion of said another
collimator leaf.
13. The radiation gantry according to claim 1, wherein an end side
of said penumbra-trimming portion facing said opposite collimator
leaf comprises a shoulder designed for running in an adapted groove
of a penumbra-trimming portion of said another collimator leaf.
14. The radiation gantry according to claim 1, further comprising a
purging magnet positioned immediately downstream of said radiation
target but upstream of said collimator for deflecting a portion of
said input radiation beam transmitted through said radiation target
into a collector.
15. A method of sharpening the penumbra of a radiation beam
comprising: generating an input radiation beam; directing and
scanning said input radiation beam onto a radiation target to form
a narrow scanned pencil radiation beam having full width of half
maximum of no more than 32 mm; sharpening a penumbra of said narrow
scanned pencil radiation beam by a collimator comprising at least
one pair of collimator leaves, wherein: a penumbra-trimming portion
of a collimator leaf facing an opposite collimator leaf of a
collimator leaf pair is made of a first metal or a first alloy of
said first metal having a first linear radiation attenuation
coefficient and said first metal has a first atomic number
according to the periodic table of the elements, said
penumbra-trimming portion having a thickness in a range of about 10
to 50 mm in the direction of said narrow scanned pencil radiation
beam; and a remaining support portion of said collimator leaf is
made of a second metal or a second alloy of said second metal
having a second linear radiation attenuation coefficient that is
lower than said first linear radiation attenuation coefficient and
said second metal has a second atomic number that is lower than
said first atomic number.
16. A radiation gantry comprising: a radiation generator for
generating an input radiation beam; a radiation target; a beam
scanning system for directing and scanning said input radiation
beam onto said radiation target to form a narrow scanned pencil
radiation beam; a collimator for sharpening a penumbra of said
narrow scanned pencil radiation beam, said collimator comprising at
least one pair of collimator leaves, wherein: a penumbra-trimming
portion of a collimator leaf facing an opposite collimator leaf of
a collimator leaf pair is made of a first metal or a first alloy of
said first metal having a first linear radiation attenuation
coefficient and said first metal has a first atomic number
according to the periodic table of the elements, said
penumbra-trimming portion having a thickness in a range of about 10
to 50 mm in the direction of said narrow scanned pencil radiation
beam; and a remaining support portion of said collimator leaf is
made of a second metal or a second alloy of said second metal
having a second linear radiation attenuation coefficient that is
lower than said first linear radiation attenuation coefficient and
said second metal has a second atomic number that is lower than
said first atomic number.
Description
TECHNICAL FIELD
The present invention generally relates to a collimator, and in
particular to a penumbra-trimming collimator useful in connection
with scanning beam therapy and beam collimation.
BACKGROUND
Approximately half of the current young generation in the Western
world will at some point in their lives be diagnosed as having
cancer and this frequency is slowly increasing. More than half of
these patients are likely to receive radiation therapy, due in
particular to the increasing use and efficacy of intensity
modulated radiation therapy (IMRT). Both the rising costs for
cancer care and the adverse side-effects in normal tissues call for
more locally effective treatment procedures such as radiation
therapy, which is undoubtedly more cost-effective and generally
more curative than both surgery or chemotherapy, and is being
recommended more and more extensively. Extensive and mutilating
surgery is now often replaced by minimally invasive surgery and
will in the future be superseded by highly precise intensity
modulated photon and light ion radiation therapy.
Improvements in tumor diagnostics, including four-dimensional
computed tomography (4D-CT), magnetic resonance imaging (MRI) and
the combination of positron emission tomography (PET) with CT
(4D-PET-CT), both enhance our knowledge about tumor spread in
relation to normal tissues and allow more precise delivery of
radiation, thereby optimizing the treatment at a reasonable
cost.
Furthermore, intensity modulated radiation therapy is rapidly
becoming the treatment of choice for most tumors with respect to
minimizing damage to the normal tissues and maximizing tumor
control. Today, intensity modulated beams are most commonly
delivered using segmental multileaf collimation, although an
increasing number of radiation therapy departments are employing
dynamic multileaf collimation. The irradiation time using dynamic
multileaf collimation depends strongly on the nature of the desired
dose distribution, and it is difficult to reduce this time to less
than the sum of the irradiation times for all individual peaks
heights using dynamic leaf collimation. Therefore, the intensity
modulation will considerably increase the total treatment time.
Document [1] discloses a collimator arrangement consisting of a
primary collimator, a multileaf collimator and two pairs of
independently adjustable block diaphragm leaves at right angles to
each other. By using rectilinear displacement of the multileaf
collimator leaves and the block diaphragm leaves, a compact
arrangement can be provided which fits into a standard collimator
head. The diaphragm leaves can, in order to reduce the cost, have a
respective inner portion made of tungsten while the remainder of
the leaves is made of lead.
SUMMARY
The present invention overcomes these and other drawbacks of the
prior art arrangements.
It is a general object of the present invention to provide a light,
compact and inexpensive collimator design.
It is a particular object of the invention to provide a collimator
suitable for usage in connection with a narrow pencil beam scanning
radiation gantry.
These and other objects are met by the invention as defined by the
accompanying patent claims.
Briefly, the present invention involves a collimator comprising at
least one pair of collimator leaves. Each leaf comprises an inner
high-attenuating penumbra-trimming portion and a remaining
low-attenuating support portion. The penumbra-trimming portion
constitutes the leaf portion in connection with the leaf end facing
the opposite collimator leaf of the leaf pair. The support portion
is then the major leaf portion facing away from the opposite leaf
of the leaf pair.
According to the invention, a provided radiation beam, such as a
photon, electron or light ion beam, preferably a narrow scanned
pencil beam, will substantially only incident on the
penumbra-trimming leaf portion. As a consequence, the material of
this inner portion has a high linear radiation attenuation
capability radiation, which is larger than the corresponding linear
attenuation capability of the support portion.
The penumbra-trimming portion is made of a first metal or a first
alloy of the first metal. The first metal has very high linear
radiation attenuation coefficient, preferably such a coefficient of
at least 1 cm.sup.-1 for photon energies of at least 50 MV. The
first metal is selected from high atomic number metals having this
high linear attenuation coefficient, such as tungsten, osmium and
iridium.
The support portion is correspondingly made of a second metal or a
second alloy of the second metal. This metal material does not have
the stringent demands on high linear radiation attenuation
coefficient as the first metal (alloy) material. As a consequence,
the linear radiation attenuation coefficient of this material is
lower than the corresponding linear attenuation coefficient of the
first metal (alloy). The second metal is selected from metals and
metal alloys having correspondingly lower atomic number as compared
to the first metal, such as iron, aluminium and steel.
Preferred materials of the penumbra-trimming leaf portion includes
high atomic number metals and metal alloys having a density of at
least 15 g/cm.sup.3. The material of the support portion does not
have the same radiation attenuating demands and is therefore, for
reducing the weight, size and cost of the collimator, preferably
made of a light metal or metal alloy materials.
A cost-effective procedure for rapid intensity modulation is using
the collimator of the present invention in connection with narrow
scanned photon, electron and light ion beams. The collimator is
then mainly employed for penumbra trimming but also for protecting
the patient body from radiation outside of a treatment volume. With
this approach, the irradiation time is largely independent of the
complexity of the desired intensity distribution and, in case of
photon beams, may even be shorter than with uniform beams. The
intensity modulation is achieved primarily by scanning of a narrow
elementary photon pencil beam generated by directing a narrow well
focused high energy electron beam onto a thin bremsstrahlung
target.
The fast low-weight collimator of the invention is capable of
further sharpening the penumbra at the edge of the elementary
scanned beam, in order to minimize the dose or radiation response
of healthy tissues. In the case of photon beams, such a collimator
can be placed relatively close to the bremsstrahlung target to
minimize its size. It can also be flat and thin, e.g. only 15-25 mm
thick in the direction of the beam with edges made of, for example,
tungsten or preferably osmium to optimize the sharpening of the
penumbra. The low height of the collimator will minimizes edge
scatter from glancing incidence. The major portions of the
collimator leafs can then be made of, for example, steel or even
aluminum (or other light metals and alloys), so that the total
weight of the collimator will be very low, such as about 10 kg,
which may even allow high-speed collimation in real time in
synchrony with organ movements.
The invention offers the following advantages: The collimator is a
perfect penumbra trimmer due to material selection; The collimator
can operate very fast; The collimator is of light weight; The
collimator can be manufactured at a low cost compared to the prior
art collimators; The collimator can easily be operated in due to
low power needs; and The collimator can be used in connection with
all radiation particle types employed in radiation diagnosis and/or
treatment.
Other advantages offered by the present invention will be
appreciated upon reading of the below description of the
embodiments of the invention.
SHORT DESCRIPTION OF THE DRAWINGS
The invention together with further objects and advantages thereof,
may best be understood by making reference to the following
description taken together with the accompanying drawings, in
which:
FIG. 1 is a schematic overview of a multileaf collimator of the
present invention seen from a top view;
FIG. 2 is a schematic overview of a pair of leaves of a multileaf
collimator according to an embodiment of the present invention;
FIG. 3 is a frontal view of an embodiment of a multileaf collimator
of the present invention along the line A-A in FIG. 1;
FIG. 4 is a schematic overview of a pair of leaves of a multileaf
collimator according to another embodiment of the present
invention;
FIG. 5 is a frontal view of another embodiment of a multileaf
collimator of the present invention along the line A-A in FIG.
1;
FIG. 6 is a schematic overview of a radiation system in which a
multileaf collimator of the present invention can be arranged;
FIGS. 7A to 7F schematically illustrate operation of the radiation
system of FIG. 6 through narrow beam scanning from different
incident angles.
FIG. 8 illustrates dose distributions of elementary 50 MV
bremsstrahlung beams for different target designs that can be used
according to the present invention;
FIG. 9 illustrates Monte-Carlo calculations of the transmission of
forward directed bremsstrahlung through different embodiments of a
multileaf collimator according to the present invention;
FIG. 10 discloses profiles of scanned and stationary photon beams
combined with collimation with a multileaf collimator according to
the present invention;
FIG. 11 illustrates characteristics of collimated and scanned
elementary photon beams in combination with a multileaf collimator
according to the present invention;
FIG. 12 illustrates the significance of employing a high density
edge to minimize the collimator electron in-scatter in connection
with electron therapy;
FIG. 13 is the Bragg curve for a typical broad therapeutic carbon
beam with energy of 400 MeV/u impinging on a tungsten collimator 30
mm in thickness;
FIG. 14 illustrates optimization of the outcome of treatment with
primary beams of varying quality utilizing uniform and scanned beam
delivery and simultaneous optimization with a single multileaf
setting for collimators of different thicknesses and edges as well
as without collimation;
FIG. 15 illustrates a comparison of treatment time for different
radiation therapy systems; and
FIG. 16 illustrates a comparison of patient throughput for
different radiation therapy systems.
DETAILED DESCRIPTION
Throughout the drawings, the same reference characters will be used
for corresponding or similar elements.
The present invention generally relates to a novel design of a
collimator having significantly reduced weight, cost and overall
size as compared to previously employed collimators. The collimator
of the present invention is in particular adapted for usage in a
radiation gantry using narrow scanned radiation beams, often
denoted a pencil-beam scanning system in the art.
The collimator of the invention comprises at least one pair of
collimator leaf. In most preferred embodiments, the collimator
comprises multiple adjacent leaves and is therefore a so-called
multileaf collimator. In the following, the collimator of the
invention is mainly described embodied as a multileaf collimator
unless mentioned otherwise. The invention, though, also encompasses
single-pair collimators that comprise one pair of two opposite
collimator leaves.
FIG. 1 is a schematic overview of a multileaf collimator 1
according to an embodiment of the present invention seen from a top
view. The collimator 1 comprises multiple, i.e. at least two but
typically about 10-100, adjacent pairs 5 of collimator leaves 10,
20. In clear contrast to the prior art, a collimator leaf 10, 20 of
the invention comprises an inner penumbra-trimming portion 12, 22
made of a first metal material and an outer or remaining support
portion 14, 24 made of a second different metal material. The inner
leaf portion 12 constitutes the end portion of the leaf 10 facing
the opposite collimator leaf 20 of the leaf pair 5. Thus, traveling
from one end of the collimator 1 through a leaf pair 5 (such as
from the left to the right in FIG. 2), one first encounters the
support leaf portion 14 made of the second material of the first
collimator leaf 10 and then, as one comes closer to the opposite
end of the first collimator leaf 10, enters the trimming leaf
portion 12 made of the first material. Thereafter, one enters the
trimming portion 22 of the second collimator leaf 20, which is also
made of the first material and then leaves this inner portion 22
and enters the support portion 24 of the second material for the
second collimator leaf 20.
As is illustrated in FIG. 1, preferably all collimator leaves 10,
20 of the collimator 1 contains a respective inner portion 12, 22
of a first material and a respective remaining portion 14, 24 of a
second material.
The characterizing feature of the collimator leaves 10, 20 of the
present invention is that the first material is a first metal
material or a first alloy material of the first metal and has a
first high linear attenuation capability or coefficient
(.mu..sub.1) [cm.sup.-1]. This material will perform the penumbra
trimming and collimating function of the collimator. As a
consequence, the material therefore preferably has very high linear
attenuation coefficient to be as thin as possible to thereby get a
sharp penumbra trimming. The trimming portion preferably has
attenuation coefficient and thickness selected so that it
attenuates at least 70%, preferably at least 75%, more preferably
around at least 80% of the incident radiation hitting the trimming
leaf portion. As a consequence, the radiation leakage is preferably
no more than 20% from this portion.
As the radiation beam will primarily only incident on the trimming
portion and not the support portion, the second material of the
support portion does not have the stringent radiation attenuation
demands as the first materials. In clear contrast, the material
selection is mainly a demand for low cost, low density and light
weight. As a consequence, the second material is a second metal
material or a second alloy material of the second metal. The second
material has lower linear attenuation coefficient (.mu..sub.2)
[cm.sup.-1] than the first material, i.e. .mu..sub.1>.mu..sub.2.
Preferably, the linear attenuation coefficient of the second
material is lower than 50% of the linear attenuation coefficient of
the first material and even lower than 25% for the first material
and still the collimator of the invention will operate
excellently.
Furthermore, the first material preferably has a high radiation
mass attenuation capability or coefficient (.mu..sub.1/.rho..sub.1)
[cm.sup.2/g] and the second material has a second radiation mass
attenuation capability or coefficient (.mu..sub.2/.rho..sub.2)
[cm.sup.2/g] that is lower than the first radiation attenuating
capability, i.e.
.mu..sub.2/.rho..sub.2<.mu..sub.1/.rho..sub.1.
For a narrow beam of mono-energetic photons, the change in
radiation beam intensity at some distance in a material can be
expressed in the form of the equation 1:
dI(x)=-I(x).times.n.times..sigma..times.dx (1) where dI(x) is the
change in intensity, I is the initial intensity, n is the number of
atoms/cm.sup.3, .sigma. is a proportionality constant that reflects
the total probability of a photon being scattered or absorbed and
dx is the incremental thickness of material traversed. Integrating
the equation and substituting n.times..sigma. with the linear
attenuation coefficient .mu. gives the expression:
I=I.sub.0e.sup.-.mu.x (2) where I is the intensity of photons
transmitted across some distance x, I.sub.0 is the initial
intensity of photons, .mu. is the linear attenuation coefficient
according to above and x is the distance traveled.
The linear attenuation coefficient (.mu.) [cm.sup.-1] describes the
fraction of a radiation beam that is absorbed or scattered per unit
thickness of the absorber. This value is of key importance for beam
collimation and basically accounts for the number of atoms in a
cubic cm volume of material and the probability of a photon being
scattered or absorbed from the nucleus or an electron of one of
these atoms. Table I lists linear attenuation coefficients for
different materials at different monoenergetic photon beams.
TABLE-US-00001 TABLE I linear attenuation coefficients (.mu.)
Photon energy Linear attenuation coefficient (cm.sup.-1) (MeV)
Tungsten Osmium Iridium Lead Iron Aluminium 1 1.28 1.52 1.52 0.80
0.47 0.17 1.25 1.08 1.27 1.28 0.66 0.42 0.15 1.5 0.97 1.14 1.14
0.59 0.39 0.14 2 0.86 1.01 1.01 0.52 0.34 0.12 3 0.79 0.93 0.93
0.48 0.29 0.10 4 0.78 0.92 0.92 0.47 0.26 0.08 5 0.79 0.93 0.94
0.48 0.25 0.08 6 0.81 0.96 0.96 0.50 0.24 0.07 8 0.86 1.02 1.02
0.53 0.24 0.07 10 0.92 1.08 1.09 0.56 0.24 0.06 15 1.04 1.23 1.24
0.64 0.24 0.06 20 1.14 1.35 1.35 0.70 0.25 0.06 50.sup..perp. 1.09
1.29 1.29 0.67 0.25* 0.06 70.sup..perp. 1.19 1.44 1.44 0.75 0.26*
0.06 *Steel .sup..perp.MV instead of MeV
The quotation of the linear attenuations of the second material and
the first material
.mu..mu. ##EQU00001## is preferably lower than 0.50, more
preferably below 0.25, especially for radiation beam energy content
of at least 1 MV, preferably at least 10 MV more preferably at
least 20 MV such as 50 MV or 70 MV.
The mass attenuation coefficient can then be calculated as the
linear attenuation divided by the density of the material:
.mu..rho. ##EQU00002##
By replacing x in equation 2 with x=y/.rho., where y is the mass
thickness of the material [g/cm.sup.2] and .rho. [g/cm.sup.3] is
the density of the material, the equation becomes:
.times.e.mu..rho..times. ##EQU00003##
Table II below lists mass attenuation coefficients for different
materials at different monoenergetic photon beams.
TABLE-US-00002 TABLE II mass attenuation coefficients (.mu./.rho.)
Photon energy Mass attenuation coefficient (10.sup.-2 cm.sup.2/g)
(MeV) Tungsten Osmium Iridium Lead Iron Aluminium 1 6.62 6.71 6.79
7.10 6.00 6.14 1.25 5.58 5.63 5.69 5.88 5.35 5.50 1.5 5.00 5.03
5.08 5.22 4.88 5.01 2 4.33 4.46 4.50 4.61 4.27 4.32 3 4.08 4.10
4.14 4.23 3.62 2.54 4 4.04 4.07 4.10 4.20 3.31 3.11 5 4.10 4.13
4.17 4.27 3.15 2.84 6 4.21 4.24 4.29 4.39 3.06 2.66 8 4.47 4.51
4.56 4.68 2.99 2.44 10 4.75 4.79 4.84 4.97 2.99 2.32 15 5.38 5.44
5.50 5.66 3.09 2.20 20 5.89 5.96 6.02 6.21 3.22 2.17 50.sup..perp.
5.64 5.70 5.75 5.93 3.15* 2.18 70.sup..perp. 6.18 6.36 6.42 6.61
3.33* 2.18 *Steel .sup..perp.MV instead of MeV
The first metal is a high atomic number metal, such as having an
atomic number of at least 72 according to the periodic table of the
elements. Preferred such high atomic number metals are the
so-called heavy metals and heavy metal alloys, such as tungsten,
osmium and iridium. In order to achieve the desired level of
radiation attenuation, the first material preferably has a density
of at least 15 g/cm.sup.3, more preferably at least 17 g/cm.sup.3,
such as around or above 20 g/cm.sup.3. Currently preferred high
atomic number materials include tungsten (W, density about 19.25
g/cm.sup.3), osmium (Os, density about 22.61 g/cm.sup.3) and
iridium (Ir, density about 22.42 g/cm.sup.3) and different alloys
thereof.
If the first material is an alloy of the first metal, such as an
alloy of tungsten, osmium or iridium, the first metal constitutes
the major constituent of the alloy. Thus, the first metal
constitutes at least 50% by weight of the alloy, more preferably at
least 60% and at least 70% by weight. In particularly preferred
embodiments, the first metal constitutes at least 80%, preferably
at least 85%, such as at least 90% or about 95% by weight of the
alloy.
The second material does not have to have the high radiation
attenuating capability of the first material but is mainly selected
for being able to support the radiation attenuating inner leaf
portion 12, 22. The second material should therefore have
mechanical properties of being able to be mechanically connected to
the first material inner portion 12, 22. Furthermore, in order to
reduce the weight and cost of the collimator 1, the second material
is preferably selected among inexpensive light metals and metal
alloys. Thus, the second metal of the second material has an atomic
number this is lower than the atomic number of the first material.
The second material preferably has an atomic number of 30 or less
according to the periodic table of the elements.
The second material preferably has a comparatively lower, more
preferably much lower, density than the first material. For
instance, the density is preferably no more than 12 g/cm.sup.3,
more preferably no more than 10 g/cm.sup.3, such as about 8
g/cm.sup.3 or below and therefore also includes low density metal
and metal alloys with density of below 5 g/cm.sup.3. Preferred
materials of the remaining leaf portions 14, 24 include steel
(density about 7.75-8.05 g/cm.sup.3) and aluminium (Al, density
about 2.70 g/cm.sup.3).
The collimator leaves 10, 30, 40 preferably have a thickness (T,
see FIG. 3) in the direction of an applied radiation beam in the
range of about 10 mm to about 50 mm. Generally, thin leaves 10, 30,
40 with a thickness (T) of only about 15 to 25 mm in the direction
of the radiation beam can be utilized. Correspondingly, the length
(L, see FIG. 1) of a collimator leaf 10 can be from about a few
centimeters up to about 30 centimeters, or even larger, and the
corresponding width (W, see FIG. 3) of a leaf 10 could be about 1
to 20 mm. The length L and width W of the collimator leaf 10 is
mainly determined based on the position of the collimator 1
relative the patient and the radiation target.
The high attenuating inner portions 12, 22 of the leaves 10, 20
only constitutes a minor portion of the total leaf volume. Thus,
the inner portion 12, 22 does not constitute more than 40 volume
percentage, preferably no more than 30 volume percentage, such as
no more than 25, 20, 15 or 10 volume percentage of the collimator
leaf 10, 20.
As is well known in the art of multi-leaf collimators, the leaves
10 of the collimator 1 are preferably individually adjustable, i.e.
can be pushed towards each other or be retracted from its
associated leaf 20 of the leaf pair 5. The leaf movement can be
linear along the longitudinal axis of the leaves 10, 20.
Alternatively, the leaves 10, 20 can be individually moved along
non-linear paths, such as a curve path, which is all well-known in
the art. FIG. 1 illustrates some collimator leaves pushed together
to prevent any significant radiation from passing through the
collimator part occupied by those leaves. However, some of the
central leaves are retracted slightly from each other to form an
opening in the collimator 1, through which a radiation beam can be
passed and simultaneously be collimated. In this way, the first
leaf portions 12, 14 will sharpen the penumbra at the edge of the
applied radiation beam in order to minimize the dose at healthy
tissue outside of an intended target volume, which is described
further herein.
FIG. 3 is a frontal view of an embodiment of the multileaf
collimator along the line A-A in FIG. 1. As can be seen in the
figure, neighboring or adjacent collimator leaves 10, 30, 40 are
provided close together, preferably touching each other's side
surfaces. This tight fitting of the collimator leaves 10, 30, 40
reduces the amount of radiation that can unintentionally leak
between adjacent leaves 10, 30, 40.
According to the leaf pair 5 embodiment in FIG. 2, the inner high
radiation attenuating leaf portions 12, 22 could have a
cross-sectional configuration in the form of a quadrate or
rectangular. FIG. 4 illustrates another possible solution for the
inner radiation-attenuating leaf portion 12. An upper portion 11 of
the inner leaf portion 12 extends a first distance from the leaf
end 15 and into the collimator leaf 10. A corresponding opposite
lower portion 13 of the inner leaf portion 12 extends a second,
shorter distance into the collimator leaf 10. As a consequence, the
side 16 of the inner leaf portion 12 facing the low-attenuating
remaining leaf portion 14 is non-perpendicular to the longitudinal
axis of the leaf 10, or expressed differently, an angle .alpha.
between the side 16 and the longitudinal axis (or lower side of the
leaf 10) is less than 90.degree. but of course larger than
0.degree.. Depending on the desired angle, the upper portion 11 can
have a distance of at least 15 mm, while the lower portion 13 has a
distance of at least 2 mm, such as at least 5 mm but is shorter
than the upper portion distance. A typical example could be to have
an upper high attenuating portion length of about 15 mm and a
corresponding lower high attenuating portion length of about 10 mm.
Such configuration of the inner portion 12 minimizes the safe size
of the portion for penumbra trimming and radiation beam blocking
point of view.
FIG. 4 also illustrates another preferred characteristic of the
high-attenuating inner leaf portion 12, 22. An end side 15 of the
inner portion 10 facing the other leaf 20 of the leaf pair 5
comprises a groove 18 designed for engagement with a matching
shoulder 28 protruding from the high-attenuating inner leaf portion
22 of the other leaf 20. This design of opposite leaf ends reduces
unintentional penetration of radiation through the leaf pair 5,
when the two leaves 10, 20 are in a closed position, pushed tight
together.
FIG. 5 is a frontal view of another embodiment of the multileaf
collimator 1 along the line A-A in FIG. 1. In this embodiment, a
first longitudinal side of the collimator leaf 10 facing a first
neighboring leaf 40 comprises a longitudinal shoulder adapted for
running in a matching longitudinal groove 40 of a facing
longitudinal side of the first neighboring leaf 40. A second
opposite longitudinal side facing a second neighboring leaf 30 is
equipped with a longitudinal groove 19 adapted for engaging a
matching longitudinal shoulder 37 provided at the facing
longitudinal side of the second neighboring leaf 30. This
collimator leaf design reduces the risk of unintentional leakage of
radiation through the small (minute) space between neighboring
leaves 10, 30, 40 in the collimator.
The concept of using shoulder and matching groove in FIGS. 4 and 5
can of course be extended so that one collimator leaf comprises
multiple grooves, multiple shoulders or at least one groove and at
least one shoulder.
The outcome of a radiobiologically optimized treatment plan can be
considerably improved by modulating the intensity of the incoming
beams. Such modulated beams can be achieved in several ways, from
the utilization of simple compensator techniques to dynamic
multileaf collimation and scanning beam systems. The most rapid and
flexible technique for non-uniform dose delivery is provided by
electromagnetic scanning of the elementary photon, electron or ion
beams in combination with dynamic multileaf collimation. If the
elementary beam is sufficiently narrow, i.e. with a FWHM (Full
Width of Half Maximum) less than about 15 mm, the influence of the
collimator on the therapeutic beam is quite low and may be viewed
as negligible or, at least, be simplified considerably in
connection with analysis of dose distributions.
The multileaf collimator of the invention is thus, in a preferred
embodiment, designed for optimal use with narrow scanned beams.
Simultaneous optimization of the scanning pattern and of the
settings on the multileaf collimator automatically steers the
elementary beam towards the opening of the collimator, thus
providing the narrowest penumbra and most effective utilization of
the beam. Consequently, the need to modulate the intensity of the
beam by dynamic collimation is reduced in a narrow beam scanning
system.
Instead, the task of the collimator becomes to protect the patient
laterally and to sharpen and cut the tails of the elementary
scanned beam. With this new role, the thickness of the collimator
can be decreased to only a few centimeters of tungsten, as an
illustrative but non-limiting example, and there is no need for
focusing edges. Such a collimator is also suitable for trimming of
light ion penumbra, since the range of carbon ions with an energy
of 400 MeV/u is around 27 mm in tungsten, in contrast to 262 mm in
soft tissue. With such penumbra trimming, the fragment tail beyond
the Bragg peak will be quite small and almost negligible, see FIG.
13. This FIG. 13 illustrates the Bragg curve for a typical broad
therapeutic carbon beam with energy of 400 MeV/u impinging on a
tungsten collimator 30 mm in thickness. These calculations were
performed employing the Shield-hit Monte Carlo code. A collimator
of this thickness stops the primary carbon beam completely.
Furthermore, the distance between the source and the isocenter can
be shortened in order to decrease the size of the elementary beam
and thereby enhance the resolution of the intensity modulated beam.
For instance, such reduction of the FWHM of the elementary photon
beam to approximately 10 mm can be employed to increase the
efficiency even further.
For all narrow scanned pencil beam applications involving photons,
electrons or light ions, a collimator edge with a thickness of
15-30 mm in the direction of the beam should generally be
sufficient. Approximately 15 mm is thick enough for high-energy
leptons (positrons and electrons), whereas the hadrons (protons and
light ions) will require leaf edges that are slightly thicker. In
the case of very narrow high-energy scanned hadron beams, leaf
collimation may not be particularly important.
However, when the penumbra of the pencil beam is enlarged in order
to minimize the scan density, penumbra trimming is still valuable.
Therefore, a collimator with a 15-25 mm leaf of osmium or tungsten
may be appropriate for universal use. Furthermore, the low leaf
height has the advantage of reducing edge scatter resulting from
glancing incidence, which could be further minimized utilizing an
edge with a slight divergence of about 5 degrees [2, 3].
Such a multileaf collimator is very light and fast compared to
those of existing designs. In comparison to the multileaf
collimators commonly used, the distance between the plane of this
collimator and the source is reduced by approximately half, which
decreases the surface area of the collimator by a factor of four.
Relative to tungsten the thickness of the absorbing material in the
collimator is only 20% and the density of steel only 40% as great
and these values become even lower if aluminum is used. The total
weight of the proposed collimator is thus only about 2% of that of
the original leaf collimator, e.g., approximately 10 kg.
For such a small collimator, the leaf is thin and inter-leaf
leakage thus higher than with a conventional multileaf collimator.
However, through usage of shoulder-groove designs at the
longitudinal sides of the leaves, such inter-leaf leakage is
significantly reduced. Furthermore, with the simultaneous use of
narrow scanned beams, only a very small fraction of the primary
beam actually hits the collimator. Consequently, interleaf leakage
is often negligible in practice.
FIG. 6 is a schematic overview of a radiation system and gantry 100
in which a multileaf collimator 1 according to the present
invention can be arranged. The gantry 100 comprises a static gantry
part 110 and a rotatable gantry part 120 that is rotatably
supported by the static part 110. In this illustrative gantry
example, the static gantry part comprises a klystron 112, such as a
50 MW klystron, for generating the driving force of a high-gradient
linac 130 provided in rotatable gantry part 120. The klystron 112
is in communication with the linac 130 through a circulator 114.
The linac 130 accelerates an electron beam 70 that is directed
towards focusing and scanning magnets 140, 152, 154 forming a beam
scanning arrangement 150 in the gantry 100. The energy content of
the electron beam 70 exiting the accelerator 130 is preferably at
least 20 MeV and more preferably at least 50 MeV.
The beam 70 is then directed towards a thin target 160 for the
purpose of generating a photon-based radiation beam 60. More
recently, the thin-target (target thinness of about 2 mm to about 5
mm) irradiation technique, which has the potential of scanning
intense quasi-Gaussian photon beams of sizes down to 12 mm FWHM at
50 MeV has been developed [4]. This is achieved using a thin
transmission target of low atomic number (preferably an atomic
number no larger than 40, such as beryllium) and, thus, low
electron scattering power so that broadening of the bremsstrahlung
beam is minimized [5, 6]. Since its FWHM is inversely proportional
to the incident electron energy, elevation of this energy from 50
to 60 MeV reduces the beam width even further.
In order to deflect the high-energy electron beam 70 transmitted
through the thin target 160, a strong purging magnet 156 should be
placed immediately below the target 160. In addition, the magnetic
field needs to be changed rapidly if the electrons are deflected
onto the same collector regardless of the direction of the photon
beam 60. This collector should absorb the electron beam, the
associated bremsstrahlung and higher-order secondary radiations
such as scattered photons and neutrons almost completely. The
geometrical size of the yoke and coils, as well as functionality
and safety issues have been discussed previously [2]. The FWHM of
the elementary photon beam at an SSD of 750 mm will be
approximately 10 mm, which means that certain conventional
beam-shaping devices, such as blocks, thick multileaf collimators
and wedges, may be redundant. However, for safety reasons and in
order to sharpen the penumbra, use of a thin multileaf collimator 1
of the invention may be desirable. Thus, the treatment head can be
made very small and compact to maintain sufficient clearance
between this head and the patient and to provide space for PET/CT
source 175 and associated equipment. An optional but preferred high
resolution dose monitor 170 may also be provided in the radiation
head.
The radiation pencil beam 60 generated at the target and having
passed through the multileaf collimator 1 of the present invention
for penumbra shaping hits a target volume in a patient 80
positioned on a patient couch 190 arranged in connection with the
radiation gantry 100. The collective operation of the beam scanning
system 150 and the fast, light multileaf collimator of the present
invention 1 allows the radiation beam 60 to be efficiently and
safely scanned over a predefined area of the patient 80 for
obtaining a rapid intensity modulated radiation therapy.
In a preferred embodiment, the gantry 100 can also be equipped with
a detector 180, e.g. an electronic portal imaging device, for
further verification of the accurate dose delivery. This detector
180 can operate together with or instead of the dose monitor 170.
The detector 180 could instead be a detector for radiotherapeutic
CT scanning using the CT scanner 175. Alternatively, the
retractable detector unit could include both a CT detector and a
portal imaging detector.
The gantry 100 illustrated in FIG. 6 should merely be seen as an
illustrative gantry design, in which the multileaf collimator 1 of
the invention can be arranged. As a consequence, the multileaf
collimator 1 can be arranged in other gantry designs and radiation
systems.
Furthermore, the electron generating source could instead be
implemented in the stationary gantry part. Other accelerator
embodiments, besides high-gradient linacs can be used, such as
racetrack microtrons [8, 9].
The proposed unit for photon and electron therapy, see FIG. 6, is
designed for rapidly adaptive, intensity modulated delivery of
radiation with a well controlled three-dimensional distribution and
is based on the unique narrow pencil beam scanning technology
together with a new principle for verification of treatment
involving advance imaging of the distributions of dose delivered by
PET-CT distributions in combination with cone-beam radiotherapeutic
computed tomography (RCT), electronic portal imaging and in vivo
monitoring of dose delivery by PET-CT and planning on the basis of
PET-RCT. However, the collimator of the invention is not limited to
this particular therapy type nor to the particular system described
above and illustrated in FIG. 6.
FIGS. 7A to 7F illustrate the operation of the radiation gantry in
FIG. 6 by directing the narrow radiation beam from different
incident angles to thereby provide a scanning of the
penumbra-shaped beam over the target volume. By being able to
rotate or turn the radiation head as illustrated in these figures,
the collimator of the invention can actually be a single leaf pair
collimator only comprising a single leaf pair.
Electromagnetic scanning with narrow bremsstrahlung beams requires
a high-energy electron beam of low emittance for purposes of
transport and photon focusing. In a recently proposed design, a
racetrack microtron was mounted on the gantry in order to reduce
the length of beam transport, as well as making the electron beam
that hits the target always is rotationally invariant and is rapid
to install [9]. Furthermore, use of a compact gantry would save
space.
Several recent breakthroughs in research on high-gradient linear
accelerators allow 50-100 MV/m accelerator gradients in both the S-
and X-band regions. This development, stimulated in part by the
suggestions for novel generation of electron and positron colliders
in connection with high-energy physics at SLAC (Stanford), KEK
(Japan) and CLIC (CERN, Geneva), was designed for large-scale
industrial manufacturing, lowering the price considerably and
making the mounting of a gantry on such accelerators of interest.
Short structures require an extremely high power peak pulse and
sophisticated engineering in order to transport the microwave from
an external klystron to the accelerator mounted on the rotating
gantry. It may also be possible to utilize a high-power magnetron
mounted in the gantry, but in this case the electron beam probably
needs to be accelerated twice in the same structure, as was done in
the Reflexotron [10].
This treatment unit described above and disclosed in FIG. 6 can
deliver optimized non-uniform beams in a very short time due to an
efficient scanning system working together with the novel
transmission target technique [5, 8]. In this fashion an elementary
electron or photon beam can be positioned electromagnetically
anywhere within a field of, for example, 40.times.40 cm.sup.2 at
the isocenter of the machine. Furthermore, the small collimator of
the present invention allows for a shorting of the distance from
the source to the isocenter, which will reduce the beam width even
more, to approximately 10 mm.
FIG. 8 illustrates dose distributions of elementary 50 MV
bremsstrahlung beams for different target designs. The narrowest
photon beam will be generated using 70 MeV initial electron beam
for instance from a short high power x-band linac mounted in the
gantry.
Monte Carlo Calculations Using GEANT4
The object oriented Monte Carlo simulation toolkit GEANT4 [11, 12 ]
was employed here to simulate particle transport through the thin
collimator of the present invention. Various 50 MV photon beams and
a 50 MeV elementary electron beam were utilized to simulate photon
transmission and electron scatter effects, respectively, in
association with collimator edges composed of various
materials.
First, collimation of photon beams by collimators composed of
aluminum and steel and with edges of tungsten or osmium was
investigated. A stationary elementary bremsstrahlung beam was
directed forward and the collimator edge positioned exactly at the
central axis. Secondly, a collimator composed entirely of tungsten
was utilized together with various incoming scanned beams. The
incoming elementary photon beam was either stationary, scanned in
parallel with or perpendicular to the collimator edges or moved
both parallel and perpendicular to the collimator edge to generate
a full and uniform beam. Moreover, the scan pattern was optimized
to produce a uniform rectangular field of 5.times.10 cm.sup.2 only
at the opening of the collimator. Here, the scan pattern of the
elementary photon beam was optimized employing an iterative
deconvolution algorithm that minimizes overdosage while always
avoiding underdosage [13]. This optimized scan pattern was then
used by the GEANT4 toolkit to simulate transmission of a scanned
photon beam through the collimator. The elementary photon beam was
generated by a 50 MeV electron beam impinging on a 3-mm beryllium
bremsstrahlung target, with programmed suppression of the
transmitted primary electron beam of high energy (49.3 MeV). The
forward stationary elementary beam was generated by at least 200
million electrons hitting the target, whereas the scanned beam was
generated by 1 billion incident electrons.
A forward directed elementary 50 MeV electron beam was employed to
simulate the in-scatter effect of electrons associated with edges
made from different materials on a steel collimator.
FIG. 9 illustrates the Monte-Carlo (GEANT4) calculations of the
transmission of forward directed bremsstrahlung through a
collimator composed of different combinations of Al and Fe and with
an edge of W or Os. The calculations for Al--W and Fe--W
collimators are presented as dotted lines, those for Al--Os and
Fe--Os as the solid (lower) lines and the uncollimated beam is
shown as the solid upper line. The beam is scored at the isocenter
and the collimator geometry depicted here is projected to this
isocenter. As expected, the Fe collimator with a 700 osmium edge
attenuates the incoming beam to a greater extent than does the Al
collimator with a tungsten edge, due to the higher densities of Os
and Fe. The tail of the narrowest beam is sharpened by both the
tungsten and the osmium edge. The Al collimator with an Os edge
adequately collimates a narrow scanned beam, whereas the Al
collimator part serves almost only as a support for the edge. Thus,
utilization of a low density material, such as aluminum, as the
primary component of the collimator in combination with a tungsten
or osmium tip is sufficient to produce an effective beam, where a
somewhat higher increase in the fluency of the transmitted
"penumbra" can be observed at the border between the tip and the
main collimator.
Multileaf Collimation of Narrow Scanned Photon Beams
The influence of designs involving multileaf collimators and leaf
tips composed of various materials on the characteristics of the
scanned photon beam was also investigated. In this context, beam
sharpening and the transmission of an elementary narrow forward
directed pencil beam (3 mm Be) were examined with aluminium (Al) or
steel (Fe) as the primary collimator material and tungsten or
osmium in the collimator tip (see FIG. 9). Particle transport was
determined by Monte Carlo simulation (GEANT4) and the beam was
generated with a 50 MeV electron beam incident onto a 3 mm Be
bremsstrahlung target. The forward directed elementary beam was
first positioned exactly at the edge of the collimator.
With identical edge thickness, a relatively high density osmium
edge attenuates the narrow beam to a greater extent than tungsten
(Table III, FIG. 9). Moreover, utilization of a low density
material such as aluminum as the primary component of the
collimator in combination with a tungsten or osmium tip is
sufficient to produce an effective beam, as shown in FIG. 9, where
a somewhat higher increase in the fluency of the transmitted
"penumbra" can be observed at the border between the tip and the
main collimator.
FIG. 10 discloses profiles of scanned and stationary photon beams
combined with a thin collimator edge. A stationary elementary beam
(solid outer line) and a profile through a scanned beam in the
y-direction without collimation (dashed outer line) are shown. The
scanned beam becomes slightly larger due to its imperfect Gaussian
characteristics. The inner lines illustrate a collimated stationary
beam (inner solid line) and a profile through a beam scanned along
the collimator edge in the y-direction (inner dashed line). The
energy fluence transmission through the thin collimator never
exceeds 20% of the primary incident beam, which is already narrow,
and can therefore be employed whenever needed to sharpen the
incident field.
FIG. 11 illustrates characteristics of collimated and scanned
elementary photon beams in combination with the collimator with a
thin edge. Monte Carlo GEANT4 calculations were used to simulate
transport through the collimator edge. The solid lines depict beams
scanned in x-direction only, while dashed lines show beams scanned
in the both x- and y-directions. The projection of the collimator
edge is positioned at the isocenter (x=0 mm). The inner solid line
illustrates an optimal scan for a desired 0-50 mm uniform field
with minimal overdosage in combination with the collimator, the
middle solid line the same situation without the collimator, and,
finally, the outer solid line shows the consequence of unnecessary
50 mm overscan in the -x direction, which results in the expected
20% uniform transmission of the primary beam. Clearly, the 80-20%
penumbra for the collimator together with the scanned beam is
sufficiently small for clinical use, in some cases even without
using the thin collimator.
The build up of tails in the integral fields for different scan
patterns is illustrated in FIGS. 10 and 11. First, a stationary
elementary beam was directed at the edge of the tungsten collimator
(solid line, FIG. 10) and scanned along the collimator tips (dashed
line). This dashed line demonstrates that the resulting integrated
beam is somewhat larger than the stationary beam (solid line), due
to its non Gaussian tail (the projected distribution of a Gaussian
beam coincides with the elementary beam). The 80-20% fluence
penumbra is no more than four our millimeters.
When the elementary beam is scanned perpendicular to the collimator
edge, the transmitted intensity penumbra is, as expected,
approximately 20% (Table III and solid line FIG. 11). When the scan
pattern generates a full uniform beam (short dashed line), (i.e.
with scanning both in parallel and perpendicular to the edge of the
collimator), the transmitted fluence of around 20% is somewhat
higher than that obtained by scanning only perpendicular to the
collimator edge. The optimally scanned beam is located solely
within the beam opening in order to minimize treatment time and
leakage from the collimator onto the patient. The resulting fluence
below the collimator edge will be maximally 20% somewhere a few
millimeters away from this edge and rapidly drop to zero at greater
distances.
Optimization of the Outcome of Photon Beam Treatment
In this case, only one optimal multileaf setting was employed
together with the different collimator designs, beam qualities and
delivery techniques, i.e., uniform beams, scanned beams involving a
full range target composed of BeW (FWHM=75 mm), a transmission
target technique using 3 mm Be (FWHM=30 mm), and, finally,
reduction of the beam size with a thinner target, higher energy and
shorter distance to obtain an FWHM of 15 mm. As the ultimate high
resolution benchmark, the size of the beam was reduced to zero in
order to obtain a point monodirectional pencil beam.
First, the treatment outcome with collimator designs involving
tungsten 15-70 mm in thickness was optimized. The thickest
collimator, which is double focusing, is used today in the
MM50-system [14, 15] at Karolinska University Hospital, Sweden and
was employed here as an almost perfect collimating system, but with
variable width of the leaves, to obtain an upper benchmark [16].
The average photon transmission of a 50 MV BeW photon beam by such
a collimator leaf is far less than 1% and has been neglected here
since it will only influence a thin rim outside of the beam
opening. The second collimator consisted of 20 mm tungsten in the
direction of the beam resulting in approximately 90% absorption and
10% transmission of the incident photon beam. The third collimator
was composed only of 15 mm tungsten, allowing transmission of 20%
of the incident beam. In addition, this latter collimator was
modified to obtain a lighter and simpler device for scanned beams
by replacing all of the tungsten by steel except at the edges
facing the beam (FIGS. 14 and 9).
As much as 60% of the full beam is transmitted through 15 mm of
steel. Obviously, conventional filtering of a uniform beam cannot
be used with either of these thin collimators, since the whole body
of the patient would be showered with transmitted photons, as seen
in the upper panels of FIG. 14. With the present MM50 collimator
design [14, 15] with a collimator of thickness 70 mm, the outcome
of treatment for uniform beams becomes about 72% while this value
was reduced to 65% in the case of the collimator composed of 15 mm
thick tungsten. Interestingly, the treatment outcome is only
reduced to 71% when the transmission through the collimator is on
the order of 10% (with 22 mm thick tungsten). The explanation for
this is simply that proximity to 10% isodose line is associated
with a large degree of tolerance by the normal tissue. Treatment of
the same patient with uniform beams using the collimator composed
of 15 mm steel and with 15 mm tungsten edges obviously leads to a
poor result, due to the far too high dose experienced almost
everywhere in the patient (upper panel in FIG. 14), as a
consequence of which the treatment outcome was reduced to
approximately 30%, i.e., by more than half in comparison to the
MM50 collimator.
When optimized scanned beams are used, the treatment outcome
rapidly improves as the elementary beam is made narrower. This is
particularly true in the case of the steel collimator, since the
elementary beam will be directed towards the collimator opening by
the algorithm for optimization of the scanning pattern. Optimal
scanning employing relatively broad elementary bremsstrahlung
beams, such as those generated from a BeW target, enhances the
treatment outcome by 6% for the thinnest collimator made of
tungsten alone and by more than 30% for the collimator composed of
steel with tungsten edges. The improvement in treatment outcome
upon replacing a uniform with a scanned beam is not as dramatic
with collimators constructed from thicker material, clearly
demonstrating that most lateral protection of organs at risk is
provided by the scanned beam, rather than by the collimator. The
combination of scanned beams using a full range target combined
with a collimator made of aluminimum does not result in an
acceptable treatment outcome.
When the width of the narrow scanned beam is reduced to below 15
mm, the treatment outcome with the thinnest collimator made of 15
mm uniform tungsten reaches a level of 81%. This value is slightly
lower for the steel/tungsten collimator and 82% for the thickest
tungsten collimator. With the narrowest beam the improvement in
treatment outcome flattens out, exhibiting almost the same value as
when the collimator possesses full thickness for the beam. In the
case of the narrowest pencil beams, the difference between a
collimator made of steel with tungsten edges and a collimator
composed completely of tungsten is negligible, since the scanned
beam itself modulates the incoming beam both longitudinally and
laterally. Thus, the collimator of the present invention can be
used instead of a heavy, expensive and cumbersome tungsten
collimator for such pencil beam radiation systems.
Interestingly, a relatively good treatment outcome is attained with
the narrowest scanned beam (FWHM=16 mm) in the absence of a
collimator (first column in FIG. 14). In general, the findings
concerning optimization using materials of higher density, such as
osmium, to construct the edge are similar, although an edge of
osmium can be somewhat thinner than when using tungsten. A
collimator edge of high density is desirable for safety reasons,
i.e., for absorbing the bremsstrahlung, electron and ion pencil
beam tail, as well as for minimizing the out-scatter of this
edge.
FIG. 14 illustrates optimization of the outcome of treatment with
primary beams of varying quality utilizing uniform and scanned beam
delivery and simultaneous optimization with a single multileaf
setting for collimators of different thicknesses and edges as well
as without collimation. The leakage is expressed as the percentage
of the primary incident energy fluence that is transmitted. Three
different elementary beams with FWHM values of 80, 32 and 16 mm
were used for scanning (middle panels) in comparison to uniform
beams (upper panel, infinite FWHM) and monodirectional point pencil
beams (lower panel, FWHM=0 mm). The first column illustrates the
optimization with scanned beams only, the second column
optimization with a scanned beam together with a steel collimator
with tungsten edges and the other three columns optimization with
collimators made of only tungsten of different thicknesses.
Multileaf Collimation of Scanned Electron Beams
The thin flat leaf collimator of the present invention is also
ideally suited for sharpening the penumbra of narrow elementary
scanned electron, as well as photon beams. Poor design of the
collimator and, in particular, of its edge may severely influence
the dose distribution in the patient as a consequence of electron
scattering by the collimator edge as well as bremsstrahlung
generated in the collimator [17, 18]. A focused collimator edge
decreases the in-scatter of nonparallel electrons, but such
in-scatter from an unfocused edge can also be largely eliminated by
hiding the edge from the source of the beam.
The build-up region is influenced by electrons that hit the
collimator on the side of the source and are then scattered out
laterally from the edge to contaminate the beam. The mean energy of
such electrons is approximately 40% of that of the incident
electrons and is independent of edge material. The dose absorbed as
a result of electron scattering is inversely proportional to the
density of this edge and almost independent of the electron energy
and atomic number [17]. Thus, the edge of the collimator should be
made of dense material such as tungsten or even osmium (Table III,
FIG. 12).
FIG. 12 illustrates the significance of employing a high density
edge to minimize the collimator electron in-scatter in connection
with electron therapy. All beam transport was simulated with the
GEANT4 transport code. The solid line depicts an uncollimated
elementary electron beam for beam scanning (at SID 70 cm) from a
compact treatment head. In this case, the beam was transported in
vacuum in order to observe the effect of the collimator edge more
clearly. The collimator was composed of steel (Fe) with a 15 mm,
high density edge of tungsten (dotted line) or osmium (dashed
dotted line). The steel edge was used as reference (dashed line).
The in-scatter by steel is roughly 5-fold higher than by tungsten
or osmium. For the osmium edge electron in-scatter is somewhat
lower than with tungsten.
For scanned electron beams, contamination by bremsstrahlung
produced in the collimator material is of lesser significance,
since more than 95% of the total primary beam is directed at the
collimator opening and only the tail of the incident elementary
beam need be collimated away. Ideally, to minimize such
bremsstrahlung, the region where the electrons enter should be
constructed of a material with a lower atomic number which however,
would unfortunately increase the lateral in-scattering of
electrons. At the same time, such in-scattering could be largely
eliminated by the use of an edge lining of high density and
thickness z.sub.1 (see Table III) [17].
Multileaf Collimation of Light Ion Beams
In the case of light ions, the design and operation of the
collimator are largely dependent on the manner by which the
incident beam is generated and the technique for range modulation
employed. The most pure dose delivery technique is by using the
narrow light ion spotscanning technique and range modulation by the
variable extracted almost monoenergetic energy elementary beam from
the accelerator. Here, the collimator of the invention functions in
a manner similar to the scanning technique for narrow elementary
electron beams. With narrow ion beams, the collimator acts more as
a safety device, both attenuating head leakage and sharpening the
tail of the lateral beam in connection with treatment. A collimator
leaf edge consisting of 30 mm thick tungsten or, even better, of
osmium (in order to minimize edge scatter [17]), completely absorbs
most light ion beams of a range of about 26 cm in water (Table
III).
The lateral scatter in connection with light ion beams can be
calculated quite accurately on the basis of a few well founded
assumptions. Assuming that the distribution of multiple scattering
[19] is Gaussian, the radius outside of which less than 1% of the
incoming particles are present, R.sub.1, is defined by the equation
5:
.intg..infin..times.e.pi..times..ltoreq. ##EQU00004## where r is
the radial displacement from the central axis of the beam (z-axis)
and r.sub.z.sup.2 is the mean square radius of the radial
distribution at depth z. Equation (5) can be integrated
analytically [17, 19] to yield the expression 6: R.sub.1.gtoreq.
{square root over ( r.sub.z.sup.w ln(100))} (6)
Since for light ion beams exhibits its highest value at the
projected range in the vicinity of the Bragg peak, equation 3 can
be simplified one step further: R.sub.1.gtoreq. {square root over
(ln(100))}.sigma..sub.r (7) where .sigma..sub.r is the variance of
the radial distribution of the pencil beam calculated at the Bragg
peak [19]. This value is distinct from the corresponding value for
electrons, which exhibit their maximal fluence and dose at
approximately half the range (z.sub.1) [17]. The radius R.sub.1 for
different collimator materials (denoted m), as well as for
different projectiles can then be approximated by simple linear
scaling with water (denoted w) on the basis of the mass scattering
power [19, 20] as follows:
.times..rho..rho..apprxeq..function..rho..rho..times..times.
##EQU00005## (assuming that no screening of the nucleus by the
orbital electrons occurs and that the size of the nucleus is
negligible).
The R.sub.1 values calculated for different collimator material and
projectiles are documented in Table III. It can be seen that the
most pronounced lateral scatter is obtained with the lightest ion
beams of lowest atomic number for which the radial variance is
highest. Furthermore, the higher the mean density of the
collimating material, the smaller the area along the front surface
of the collimator that can scatter ions away from the front edge,
again pointing to osmium as the most interesting collimating
material.
Quite often, in order to avoid having to deliver a very large
number of beam spots in the total scanning pattern, light ion
pencil beams are not generally focused so as to obtain minimal
diameter. With such focusing multileaf trimming of the penumbra
allows significant improvement of the quality of the beam at its
edge, as well as enhanced elimination of over-scanning. Similarly,
when ion beams accelerated in a cyclotron are decelerated for
appropriate range modulation, the emmitance selection system will
be more efficient when slightly larger beam spots are allowed.
As is illustrated in Table III, the preferred materials of the
penumbra-trimming portion of the leaves have low values (Z.sub.1 in
the table) of any longitudinal spread of an incident radiation beam
in the trimming material. This means the risk of contaminating the
radiation therapy beam through such spread radiation originating
from multiple scattering in the materials is therefore
significantly reduced.
TABLE-US-00003 TABLE III radiation-related material characteristics
PHOTONS LIGHT IONS COLLIMATOR 50 70 ELECTRONS .sup.1H .sup.9C
.sup.11C .sup.12C .sup.1H .sup.- 12C Energy MV MV 50 70 210 400
Quan- .mu./.rho. .mu./.rho. MeVe.sup.- MeVe.sup.- MeV MeV/u 210 400
tity .rho. 10.sup.-2 t.sub.1% t.sub.10% t.sub.20% 10.sup.-2
t.sub.1% t.sub- .10% t.sub.20% z.sub.csda z.sub.1 z.sub.csda
z.sub.1 R R.sub.1 Unit Z g/cm.sup.3 cm.sup.2/g mm cm.sup.2/g mm mm
mm mm mm H.sub.2O 7 1.0 1.88 2450 1220 856 1.85 2489 1240 870 198
144 255 176 278.5- 209.0 255.4 278.7 15.1 4.2 Be 4 1.8 1.22 2040
1020 713 0.93 2677 1338 935 143 113 187 141 186.7 140.5- 171.8
187.4 7.0 1.9 C 12 1.7 1.64 1652 826 577 1.53 1370 684 478 134 98
172 93 139.5 104.9 128- .2 139.8 19.8 5.5 Al 13 2.7 2.18 782 391
273 2.18 782 391 273 77.4 48 96.2 56 133.2 99.4 121- .5 132.6 9.0
2.5 Steel 26 7.8 3.15 187 94 66 3.33 177 89 62 23.8 12 28.5 13.6
50.4 37.5 45.- 8 50.0 4.3 1.2 W 74 19.3 5.64 42 21 15 6.18 39 19 13
7.8 2.8 8.9 3.1 28.1 20.8 25.4 27.7 - 2.7 0.7 Os 76 22.6 5.70 36 18
12 6.36 32 16 11 6.7 2.4 7.6 2.6 24.5 18.1 22.1 24.1- 2.4 0.6 Hg 80
13.5 5.88 58 29 20 6.48 52 26 18 10.9 3.9 12.4 4.3 41.2 30.4 37.1
40- .5 4.1 1.1 Pb 82 11.4 5.93 68 34 24 6.61 61 31 21 12.8 4.6 14.6
5.0 49.4 36.5 44.6 48- .6 4.9 1.3 U 92 18.9 6.22 39 20 14 6.95 35
18 12 7.6 2.6 8.7 2.9 30.6 22.6 27.6 30.1 - 3.1 0.8
Radiobiological Optimized Treatment Planning
The influence of different collimator designs on the outcome of
treatment with scanned beams was examined here with our treatment
planning pencil beam optimization algorithm [21]. This versatile
algorithm employs constrained iterative optimization of the
settings on the multileaf collimator and the scanning pattern
simultaneously [21-25]. For each collimator design, a relatively
simple transmission function that takes into account only the
attenuation of the primary beam is incorporated into the algorithm.
For the sake of simplicity, this transmission function involved
only a tungsten edge with a width of 15 mm and no tapering such as
that in the more optimized design depicted in FIG. 1B.
Our optimization algorithm [13, 21] utilized the probability of
complication free control of the tumor, P+, as an indicator of the
treatment outcome. The target volume was a stage IV cervix cancer
with spreading to lymph nodes and a volume of 64.times.64.times.24
cm.sup.3 with a cubic voxel size of 0.5.times.0.5.times.0.5
cm.sup.3 was studied. Relevant radiobiological data were obtained
from the literature [16, 26, 27].
In order to demonstrate the efficiency of this collimator design in
combination with pencil beam scanning, optimal radiobiological
treatments of an advanced cervix cancer was simulated. Different
geometrical collimator designs were tested for bremsstrahlung,
electron and light ion beams. With a 10 mm half width elementary
scanned photon beam and a steel collimator with tungsten edges, it
was possible to make as effective treatments as obtained with
intensity modulated beams of full resolution, i.e. near 5 mm
resolution in the fluence map. In combination with narrow pencil
beam scanning, such a collimator may provide ideal delivery of
photons, electrons or light ions for radiation therapy synchronized
to breathing and other organ motions. These high-energy photon and
light ion beams may allow 3-dimensional in vivo verification of
delivery and thereby clinical implementation of the BIOART approach
using Biologically Optimized 3-dimensional in vivo predictive Assay
based adaptive Radiation Therapy [33].
Fast Intensity Modulated Treatment
The continuously increasing incidence of cancer and associated
costs for health care call for more rational and cost-effective
methods of treatment. Busy and efficient clinics require more
rapid, more accurate and most cost efficient techniques for dose
delivery. Conventional radiation treatments employing static
uniform beams that are still in use at most centers for radiation
therapy centers take approximately 10-15 minutes from the time the
patient enters the treatment room until he/she has left. Most of
this time is devoted to positioning the patient, quality assurance
and care. The period of radiation, including rotation of the
gantry, is about 1-3 minutes, depending on the type of equipment
and technique employed. Most treatment units of this type are
designed to treat as many patients as possible with a given
time-frame.
Introduction of intensity modulated radiation treatment into the
clinic requires more sophisticated quality assurance with respect
to the delivery of beams, due to uncertainties in the positioning
of the patient and organ movement. Most equipment in use today
involves relatively old gantry technology and beam shaping designs,
even though beam modulation has been improved considerably by
dynamic multileaf collimation. Consequently, more time must be
spent both on positioning the patient and delivering the IMRT
treatment.
More integrated solutions, in which planning of the treatment,
movement of the target (e.g. due to respiration) and the
characteristics of the beam are integrated on-line, would be highly
advantageous. Today, these parameters are integrated primarily by
using external markers and margins for positioning. The
relationship to the actual clinical target volume during treatment
is less well-defined and generally based on addition of an internal
margin and, in some cases, stereotactic beam alignment on small
targets [28].
Today, most new therapy units being installed are capable of
performing IMRT, being equipped with multileaf collimators that can
be operated in a dynamic mode with segmental steps and the shoot
technique and, in certain cases, even continuous dynamic velocity
modulation. Such velocity modulation of the intensity of multileaf
collimation is most rapid and exhibits high resolution. However,
the period of irradiation required is still proportional to the sum
of the differences between consecutive peaks and valleys in profile
of the beam delivered. Thus, a highly complex irradiation involving
multiple peaks in the beam profile, the time of irradiation may be
several-fold longer than that require for conventional treatment
with a uniform beam. In contrast, a scanned ultra narrow beam, on
the other hand, with an average rate of dosage similar to that
employed for a broad scanned or conventional flattened beam will be
only minimally influenced by the complexity of the incident energy
fluence profile. Fast pencil beam scanning systems are
approximately three orders of magnitude faster than mechanical
devices such as those involving blocks or multileaf collimation and
can produce a beam with high resolution within a second. The novel
collimator of the present invention having a low weight described
herein is also potentially much faster than conventional multileaf
collimators, with potential speeds of approximately 10 cm/s or
more, and furthermore needs to move shorter distance to obtain only
a few multileaf settings.
4D-intensity modulated radiation therapy involving adaptive therapy
approaches or other more dynamic techniques that take breathing
and/or the movement of internal organs into account requires more
rapid techniques for delivery in order to be cost-effective. In the
case of intensity modulated beams employing dynamic multileaf
collimation, the required irradiation time is proportional to the
complexity of the modulation; whereas, in contrast with narrow
scanned beams, this irradiation time is almost independent of the
dose variations in the beam and more dependent on the total mean
energy imparted. With increased use of strong intensity modulation,
the irradiation time with conventional IMRT techniques will account
for a larger portion of the total treatment time.
It has been shown [9] that for therapy involving fast modulation of
the intensity of photon beams, electromagnetic scanning is
advantageous. Here, characteristics of the novel multileaf
collimator designed to narrow scanned elementary photon pencil
beams have been presented in connection with an advanced cervix
cancer. For most narrow elementary beams, where the influence
exerted by the collimator is relatively low, a steel or aluminum
collimator with tungsten or osmium edges is sufficient to attain
the best possible outcome of the treatment. Our findings strongly
motivate the development of such fast collimators. Together with
narrow scanned beams, such collimators are potentially useful for
real time adaptive therapy and interestingly very similar designs
may be employed for therapy with photons, electrons and light
ions.
Other Gantry Designs
As was mentioned in the foregoing, the collimator of the present
invention can be used in connection with the Orbiter system [29].
The key characteristics of the Orbiter are: high speed delivery of
high precision conformal, intensity modulated radiation therapy;
accurate patient positioning through built in laser camera [30];
automated fixed field "multi segmented" therapy; dynamic intensity
modulation with high resolution Multi-Leaf Collimator ("MLC") or a
newly developed areal modulator; no risk of collision between
treatment head and patient; beam clearness in all gantry angels;
and high reliability and low cost per treatment.
Orbiter has currently only one energy--the 6 MV photon beam. The
accelerator is placed in line close to the target in the treatment
head. The gantry is capable of unprecedented high-speed rotation.
The system will be designed for gantry speeds of up to 10 rotations
per minute, which means 10 times faster than existing systems. The
design of the gantry will allow fast acceleration and
retardation.
The gantry has two support points. This implies better mechanical
gantry stability, which means better isocentric precision. The
gantry has no end-up, allowing full rotational freedom. This means
that the shortest possible route from one gantry angle to the next
can always be chosen. This will save time. In addition, it may
facilitate rotational treatment techniques such as arc therapy or
tomotherapy, although the Orbiter is not primarily designed with
such treatment techniques in mind.
The MLC is designed for intensity modulation. The field size should
be at least 30 cm.times.40 cm, with a projected leaf width of 7.5
mm. The leaves should have a very large over travel, 150 to 200 mm,
so that large field sizes can be intensity modulated. The leaf
speed should be high, more than 25 mm per second, to facilitate
effective delivery of intensity modulated treatment fields.
Optionally the system can be equipped with a two dimensional
hexagonal areal intensity modulator allowing fast beam flattening
and/or intensity modulation.
Collision between gantry and patient is not possible, because all
moving parts are hidden inside the gantry. The couch will only be
adjusted small distances in the lateral and vertical direction.
The couch has a very low radiation cross-section in the treatment
area, allowing beams to be delivered from all gantry angles without
restriction. This is made possible by the fact that the couch has
two support points.
The non-existent beam transport results in low cost and high
reliability.
The electronic portal imaging device based on GEM technology is an
integral part of the system and enclosed inside the system. It will
produce both diagnostic and therapeutic images of high quality
The Orbiter can be interfaced to the most commonly used Treatment
Planning Systems. The Orbiter can also be interfaced to the most
common verification systems. The collimator of the present can
advantageously be used in the Orbiter system, preferably also
together with the dynamic beam intensity modulator disclosed in the
document [31].
In a further implementation embodiment, the collimator of the
invention is used in connection with the BioARTist system described
herein.
More than half of all cancer patients benefit from radiation
therapy and the number is steadily increasing. Modern biologically
based intensity modulated treatment techniques might improve the
treatment outcome by as much as 20-30% for advanced resistant
tumors. More advanced diagnostic and therapeutic instruments are
necessary particularly for complex hypoxic or otherwise radiation
resistant tumors to improve the uncomplicated tumor control.
Sensitive and specific tumor imaging techniques such as PET-CT and
more tumor specific tracers will allow accurate delineation of the
tumor spread. Accurate target definition and radiobiological
response information is paramount for radiobiological based
treatment planning and precise dose delivery. Advanced treatment
monitoring and verification methods for tumor response and dose
delivery will assure maximum treatment quality when combined with
biologically based treatment optimization. Also more dynamic
properties of the treatment should be taken into account in the
optimization process, such as organ motion, patient specific tumor
responses during the cause of the treatment. Thus the therapeutic
monitoring of the tumor by new dedicated image modalities such as
PET-CT are important for the clinical outcome. High quality
radiation therapy will in the future be based on sensitive tumor
diagnostic such as PET-CT imaging. This will allow
radiobiologically treatment optimized for high precision radiation
therapy delivery and on-line treatment follow up using PET-CT
therapeutic imaging for predictive assay based adaptive treatment
optimization.
The BioArtist diagnostic therapy system is fully developed for
clinical implementation of the BioArt concept. The system is a full
integration of a therapy unit optimized for precise and high speed
IMRT using narrow scanned photon beam with a diagnostic PET-CT
tumor camera for in vivo therapeutic dose delivery imaging. Such a
system will allow on-line treatment follow up of tumor spread,
radiation sensitivity and in vivo dose delivery for adaptive
treatment optimization. As this system utilizes narrow scanned
photon beams, it will benefit from usage of the collimator of the
invention. FIGS. 15 and 16 is a schematic overview of the BioArt
treatment unit.
A new therapy strategy called BIO-ART, Biologically Optimised 3D-in
vivo predictive Assay based Radiation Therapy is now being
developed at the Karolinska Institutet, Sweden, and the Biocare
consortium. The concept is based on PET-CT imaging of the tumor
before radiation therapy and at early time during the actual
IMRT-radiation therapy treatment to pick up the tumor
responsiveness to the treatment and adaptively change the treatment
to maximize the treatment outcome as illustrated in the figure.
Initially, the patient is administered FDG (fluorodeoxyglucose) or
more tumor specific tracers for PET-CT tumor imaging. The patient
is treated for about 3-5 treatment fractions using biologically
optimized intensity modulated therapy planning before a repeated
PET-CT image is recorded to get tumor responsiveness data early on
in the treatment after. About 3 to 5 treatment fractions later
where still meaningful tumor imaging is feasible, the last PET-CT
patient specific data set for the Predictive Assay of the tumor
responsiveness is recorded to get a better knowledge of the
influence of the rate of loss of functionality of the doomed tumor
cells. A final revised treatment plan is made based on the tumor
cell distribution and responsiveness image data sets. A high
resolution and high sensitive PET-CT camera is developed also for
integration in a therapy unit, a diagnostic therapy unit PET-CT-RT
unit to allow simultaneously delineation of tumor spread as well as
therapeutic imaging of the in vivo delivered dose distribution to
exactly correlate the delivered dose to the tumor response in
actual the treatment position.
This integrated PET-CT camera will allow in vivo dose delivery
imaging of the patient in treatment position to be overlayed on the
tumor cell density image and allow accurate dose delivery
verification and treatment optimization based on actual 3D in vivo
dose delivery and tumor responsiveness data.
The new diagnostic radiation therapy is designed for fast cost
effective adaptive intensity modulated radiation therapy and is
ideal for modern treatment protocols like BioArt: The on-board high
sensitivity and high resolution PET-CT camera will allow in vivo
tumor diagnostics imaging for accurate delineation of the local and
regional tumor spread and responsiveness as well as the delivered
dose distribution. The narrow high energy photon beams generates a
very positron emitter activity by photonuclear reactions in the
patient to allow accurate in vivo verification of the delivered
dose distribution in 3D using the same high sensitivity PET-CT
camera as used for the initial tumor diagnostics. The total
delivered dose distribution during fractionated radiation treatment
can be optimally controlled by adaptation of the integrated dose
delivery to the initial biologically optimized treatment plan tumor
spread distribution, and the monitored tumor responsiveness to
drastically increase both the quality and safety of the treatment,
based on the BIO-ART strategy. Fast pencil beam scanning technology
offers a unique possibility to image the dose delivery and geometry
of the whole patient volume in 3D using the relatively high pair
production contrast by combined PET and radiotherapeutic-computed
tomography. The fast narrow photon and electron pencil beam
scanning system integrated with a new ultra fast portal imager will
allow improved patient set-up as well as dynamic dose delivery
locking on a moving tumor in real time. The beam scanning system
can also be auto-calibrated and use real time dosimetric
verification with a segmented high-resolution transmission monitor.
The irradiation time using narrow scanned beam is practically
independent of the complexity of the desired dose distribution in
contrast to IMRT-delivery using multi-leaf collimation where the
treatment time is proportional to the complexity of the given
fields. Built in auto calibration system and remote check and
confirm system. Ergonomically designed treatment unit convenient to
work around due to low height of tabletop. The overall compact
therapy unit size will save space in the treatment room.
For patients the systems described herein are offering a number of
benefits, which implicitly translates into benefits for the clinic.
These are:
Higher precision: Not only do Orbiter and BioArtist with their
unique dual pivot couches [32] and solid stationary gantry designs
offer a mechanically more stable treatment machine, but the
built-in diagnostic and therapeutic imaging systems also allow for
future biologically optimized adaptive treatment techniques.
Increased safety: With the inherent safe non-moving mechanical
design any risk of collision is eliminated.
Ergonomic design: Both treatment units are compact and allowing
close contact with the patient.
High patient throughput: The unique properties of the systems allow
for up to 100% faster treatments, which is illustrated in FIGS. 15
and 16. FIG. 15 illustrates a comparison of treatment time (in
minutes) for different radiation therapy systems and FIG. 16
illustrates a comparison of patient throughput (patients per hour)
for different radiation therapy systems.
Low life cycle cost: The compact mechanical design of Orbiter and
BioArtist will ensure high reliability and cost effective
treatments.
Both systems are dedicated for modern treatment techniques like
IMRT and adaptive radiation therapy but can also be used for
conventional radiation therapy.
It will be understood by a person skilled in the art that various
modifications and changes may be made to the present invention
without departure from the scope thereof, which is defined by the
appended claims.
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